The origin of your bass was China. You and the bass now live in Rego Park, Queens...an area I'm quite familiar with. I grew up in Woodside, worked fixing guitars at Sam Ash Music in Forest Hills until 1982.
Anyway, In Reno- Lake Tahoe, where I repair basses now, we see huge fluctuations in humidity. It can be as low as 13% in the summer. Yeah, you read right. It is currently 71% humidity in my shop. I repair a LOT of humidity, NOT temperature related cracks. The basses I see usually are cracked somewhere, due to a dramatic change in the humidity, or the ALTITUDE where the bass is stored, versus the area where the bassist uses it. Lake Tahoe is 6,500 feet above sea level, and Reno is 4,420. We seldom see a 2,000 foot difference in altitude from gig to home in N.Y. It is quite common here.
I have to retune my Lowendall carved bass when I play in Truckee, or South Lake Tahoe. I would guess Rego Park is about a hundred feet or so, above sea level- or close to it.
The Chinese factory, or luthier's shop your bass came from, is kept at what humidity? What altitude? We do not know. What kind of drying method do they use for the billets of wood used in the making of their basses?
I have seen an inferior grade defective maple billet used in a hybrid Sunrise bass, but am not familiar with the higher priced Chinese basses. I would say, it is possible that the piece of wood used to carve the top, was not properly acclimated, or suffered a humidity-drying out related crack exacerbated by pressure from the post and the bridge. After arriving here, in The U.S., as it acclimated to the Queens area, things weren't quite the same as in their shop, or geographical area. The post just helped it open up. The top patch, installed from the outside, through the 'F' hole, and reduction in soundpost length is a very stable, strong repair done by a good bass luthier. I've done quite a few, never had one come back. Good luck with your bass!
